Spread spectrum communication equipment

ABSTRACT

A spread spectrum communication equipment comprises a correlator outputting a correlation output signal, a timing generator generating two timing signals in response to a correlation peak value, detecting circuits for detecting information of a correlation output signal based on either one of the timing signals, receiving information detected in either one of the detecting circuits and checking whether the information coincides with the ID code, a switching circuit for selecting connection or disconnection between the detecting circuits and a demodulator, and a control circuit responsive to outputs of the checking circuits for selecting connection or disconnection with the switching circuit.

FIELD OF THE INVENTION

The present invention relates to a spread spectrum communicationequipment, and more particularly to a spread spectrum communicationequipment into which, if a plurality of receiving signals each having adifferent identical code, only those having the same ID code as that ofthe equipment itself can be inputted.

BACKGROUND OF THE INVENTION

In a communication equipment based on a spread spectrum communicationsystem, characteristics such as resistance to interference or securityof signals are improved by subjecting information signals, such as voiceor data, to be transmitted in a form of code spreading using a PN code(spreading code) in the transmitting side to convert them to signalshaving a broader spectrum than that originally occupied by the signals,for transmission.

For this reason, in a spread spectrum communication equipment in thereceiving side, it is necessary to execute so-called the reversespreading in which the received signals are subjected to correlationdemodulation by generating the same PN code as that in the transmittingside to compress the spreaded spectrum to a frequency spectrum.

For that purpose, in order to generate the same PN code in the receivingside at the same timing as in the transmitting side, a correlation peakvalue is extracted from a receiving signal by making use of the factthat PN code has sharp self-correlating characteristics, and a timingsignal is generated to synchronize the PN code with respect to aposition of the correlation peak value.

With the conventional type of spread spectrum communication equipment asdescribed above, however, if a plurality of spectrum spreadingcommunication equipments each using the same PN code are usedsimultaneously, correlation outputs (spreading reverse outputs) due tointerference from the transmitting side are detected in the receivingside. For this reason, it is impossible to detect a correlation peakvalue produced by a receiving signal from a desired station (a partnerstation in the receiving side with which it is desired to communicate),which disadvantageously disables the communication.

In other words, with the conventional type of spread spectrumcommunication equipment, if a plurality of spread spectrum communicationequipments each using the same PN code are used simultaneously,sometimes communication with a desired station may become impossible.

FIG. 4 and FIG. 5 show the problems as described above. That is in acase where two units of spread spectrum communication equipments(described as "transmitting side TX1, TX2" hereinafter) each using thesame PN code exist in the transmitting side and also two units ofspectrum spreading communication equipments (described as "receivingside RX1, RX2 " hereinafter) each using the same PN code as that in thetransmitting side above exist in the receiving side, assume as shown inFIG. 4 that sending power from the transmitting side TX1 to thereceiving side RX1 is f1, sending power from the transmitting side TX2to the receiving side RX2 is f2, interference power from thetransmitting side TX1 to the receiving side RX2 is If1, and interferencepower from the transmitting side TX2 to the receiving side RX1 is If2.As the receiving side RX1 receives the sending power f1 from thetransmitting side TX1 and the interference power If2 from thetransmitting side TX2, two correlation peak values, namely a correlationpeak value due to If2 and that due to f1, exist in a form of correlationoutput (not shown herein) as shown in FIG. 5. For this reason, itsometimes is impossible to accurately detect a correlation peak valuefor the transmitting side TX1 which is a desired station, and, in turn,it disables the communication with the desired station.

SUMMARY OF THE INVENTION

It is an object of the present invention to ensure communication with adesired station even if a plurality of spread spectrum communicationequipments each using the same PN code are used simultaneously.

A spread spectrum communication equipment according to the presentinvention, generates at least one timing signal in response to acorrelation peak value existing in a correlation output signal outputtedfrom a correlating means by using information on the correlation outputsignal detected by a plurality of detecting means according to one ofthe timing signals respectively. A determination is made by a pluralityof confirming means as whether the information detected by eachdetecting means coincides with the ID code previously stored therein. Acontrol means receives a confirmation from the plurality of confirmingmeans and connects a detecting means, to a demodulating means toselectively input and demodulates only receiving signals having the sameID code as that of for the equipment from a plurality of receivingsignals each having the same PN code and different ID codes.

The spread spectrum communication equipment according to the presentinvention generates, in response to a correlation peak value existing ina correlation output signal outputted from a correlating means a timingsignal corresponding to the correlation peak value with information inthe correlation output signal detected by a detecting means according tothe timing signal, and then makes a determination with a checking meansas to whether the information coincides with the ID code previouslystored therein. A switching means selects connection or disconnectionbetween the detecting means and a demodulating means based on a resultof checking by an ID checking means. Also a timing generating meansreceives a result of checking by the ID checking means and generates,when the ID code is not identical and also another correlation peakvalue exists in a correlation output signal outputted from a correlatingmeans, a timing signal based on the other correlation peak value. As aresult, the spread spectrum communication equipment according to thepresent invention selectively inputs and demodulates only receivingsignals having the same ID code as that of the equipment from aplurality of receiving signals each having the same PN code anddifferent ID codes.

Other objects and features of this invention will become understood fromthe following description with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a spread spectrum communication equipmentaccording to Embodiment 1 of the present invention;

FIG. 2 is a drawing for explaining a correlation output signal (a signalindicating a correlation peak value delayed by time t) outputted from acorrelator;

FIG. 3 is a block diagram of a spread spectrum communication equipmentaccording to Embodiment 2 of the present invention;

FIG. 4 is a drawing for explaining the problems in a conventional typeof spectrum spreading communication equipment; and

FIG. 5 is a drawing for explaining the problems in a conventional typeof spectrum spreading communication equipment.

DESCRIPTION OF THE PREFERRED INVENTION

A detailed description for the spread spectrum communication equipmentaccording to the present invention in the order of Embodiment 1 andEmbodiment 2 is made with reference to the drawing.

In FIG. 1, Embodiment 1 of the present invention comprises: a correlator101 which detects correlation between a received spreading code (PNcode) included in a received signal and a spreading code 102 generatedat the receiving side (reference PN code), and outputs a correlationoutput signal; a timing generator 103 which generates two timing signalst1, t2 in response to the two correlation peak values existing in acorrelation output signal outputted from the correlator 101; detectingcircuits 104, 105 each detecting information of a correlation outputsignal outputted from the correlator 101 according to one of the timingsignals t1, t2 generated by the timing generator 103; a checking circuit107 for inputting thereinto the information detected by the detectingcircuit 104 and checking whether the information coincides with the IDcode 106 previously stored therein; a checking circuit 108 for inputtingthereinto the information detected by the detecting circuit 105 andchecking whether the information coincides with the ID code 106previously stored therein; a switching circuit 109 provided between thedetecting circuits 104, 105 and a demodulator 111, described later, forselecting connection or disconnection between the detecting circuits104, 105 and the demodulator; a control circuit 110 for inputtingtherein a result of checking by the checking circuits 107, 108 andselecting connection or disconnection by the switching circuit 109; anda demodulator 111 for demodulating a signal inputted through theswitching circuit 109.

With the configuration described above, now description is made foroperations thereof. In the spread spectrum communication equipmentaccording to Embodiment 1, when two signals each having the same PN codeas that for the equipment but also having different ID codes arereceived, or more specifically when receiving signals each having thesame PN code as. PN code 102 for the equipment but also having differentID codes ID1 or ID2 respectively are received, at first the correlator101 executes reverse spreading using the PN code 102 and, as shown inFIG. 2, outputs a signal indicating a correlation peak value displacedby time t as a correlation output signal. Herein the time t correspondsto a time lag between timings for sending powers by two units of spreadspectrum communication equipment having the same PN code 102 in thetransmitting side.

The timing generator 103 generates, when a correlation output signalindicating correlation peak value displaced by time t is inputtedthereinto from the correlator 101, timing signals (timing pulse array)t1, t2 having a PN cycle displaced by the time t according todisplacement of these correlation peak values, and outputs the timingsignals t1, t2 to the detecting circuits 104, 105.

The detecting circuit 104 receives a correlation output signal from thecorrelator 101, detects information of the correlation output signalaccording to the timing signal t1, and outputs the information to thechecking circuit 107 and the switching circuit 109. Similarly thedetecting circuit 105 receives a correlation output signal from thecorrelator 101, detects information of a correlation output signalaccording to the timing signal t2, and outputs the information to thechecking circuit 108 and the switching circuit 109.

The checking circuits 107, 108 compare the inputted informationthereinto respectively with the ID code 106 to check whether theinformation coincides with the ID code 106, and outputs a result ofchecking to the control circuit 110.

When receiving a result of checking from the checking circuits 107, 108,the control circuit 110 controls the switching circuit 109 so that anoutput from a detecting circuit (104 or 105) corresponding to a checkingcircuit (107 or 108) determined as having the same ID code as the IDcode 106 is sent to the demodulator 111.

With this configuration, a received signal having the same PN code asthat of the equipment and also having the same ID code is outputtedthrough the switching circuit 109.

As described above, the spread spectrum communication equipment can onlyexecute communication with a partner station having the same PN code asthat of the equipment and also having the same ID code even if twosignals each having the same PN code as that of the equipment but alsohaving a different ID code are inputted.

Although the description of Embodiment 1 assumes a case where there isonly one interfering station, it is clear that the same effects can beachieved by increasing a number of detecting circuits as well as anumber of checking circuits even in a case where there are a pluralityof interfering stations as shown in FIG. 1.

FIG. 3 is a block diagram of a spread spectrum communication equipmentaccording to Embodiment 2 of the present invention comprising: acorrelator 101 which detects correlation between a received spreadingcode (PN code) included in a received signal and a spreading code 102generated the receiving side (reference PN code) and outputs acorrelation output signal; a timing generator 301 which generates asignal ti corresponding to a correlation peak value in response to acorrelation peak value existing in a correlation output signal outputtedfrom the correlator 101; a detecting circuit 302 for detectinginformation on a correlation output signal outputted from the correlator101 according to the timing signals ti generated by the timing generator301; a checking circuit 304 receiving the information detected by thedetecting circuit 302 and checking whether the information coincideswith the ID code 303 previously stored therein; a switching circuit 305provided between the detecting circuit 302 and a demodulator 111,described later, for selecting connection or disconnection between thedetecting circuits 302 and the demodulator 111; and a demodulator 111for demodulating an signal inputted through the switching circuit 305.

With the configuration described above, now description is made foroperations thereof. In the spread spectrum communication equipmentaccording to Embodiment 2, when two signals each having the same PN codeas that of the equipment but also having different ID codes arereceived, or more specifically when receiving signals each having thesame PN code as PN code 102 of the equipment but also having differentID codes ID1 or ID2 respectively are received, at first the correlator101 executes reverse spreading using the PN code 102 and outputs asignal indicating a correlation peak value displaced by time t as acorrelation output signal. Herein the time t corresponds to a time lagbetween timings for sending powers by two units of spread spectrumcommunication equipment having the same PN code 102 in the transmittingside.

The timing generator 301 generates, when a correlation output signalindicating correlation peak values displaced by time t is inputtedthereinto from the correlator 101, two timing signals (timing pulsearray) having a PN cycle displaced by the time t according todisplacement of these correlation peak values, and outputs timingsignals to the detecting circuit 302 as a timing signal ti.

The detecting circuit 302 receives a correlation output signal from thecorrelator 101, detects information of the correlation output signalaccording to the timing signal ti, and outputs the information to thechecking circuit 304 and the switching circuit 305.

The checking circuit 304 compares the inputted information thereintowith the ID code 303, checks whether the information coincides with theID code 303, and in response generates a signal to the timing generator301 and the switching circuit 305.

The switching circuit 305 selects connection or disconnection accordingto this signal from the checking circuit 304.

The timing generator 301 after receiving the output signal from thechecking circuit 304, outputs, when the ID code does not coincide andalso another correlation peak value exists in a correlation outputsignal outputted from the correlator 101, a timing signal based on thelatest correlation peak value to the detecting circuit 302 as a timingsignal ti. The detecting circuit 302 and the checking circuit 304 make adetermination with the new timing signal ti as whether the ID codecoincides with the ID code 303.

With the sequence of operations as described above, a receiving signalhaving the same PN code as that of the equipment and also having thesame ID code is outputted from the switching circuit 305.

As described above, in Embodiment 2, even if two receiving signals eachhaving the same PN code as that of the equipment but also havingdifferent ID code are inputted, communication with a partner stationhaving the same PN code as that of the equipment and also having thesame ID code can only be executed without fail.

Although description of Embodiment 2 assumes a case where there is onlyone interfering station, it is clear that the same effect can beachieved even in a case where there are a plurality of interferingstations.

As described above, the spread spectrum communication equipment,according to the present invention, has a correlating means fordetecting a correlation between a received PN code included in areceiving signal and a reference PN code generated the transmitting sideand outputting a correlation output signal, and a demodulating means forreceiving and demodulating the correlation output signal. A timinggenerating means generates at least one timing signal in response to acorrelation peak value existing in a correlation output signal outputtedfrom the correlating means. A plurality of detecting means each detectsinformation of the correlation output signal outputted from thecorrelating means based on one of the timing signals generated by thetiming generating means. A plurality of ID checking means each receivesinformation detected by the detecting means and checks whether theinformation coincides with ID code previously stored therein. Aswitching means provided between the plurality of detecting means andthe demodulating means selects connection or disconnection between theplurality of detecting means and the demodulating means. A control meansfor receiving a result of checking by the plurality of ID checking meansselects connection or disconnection of the switching means. Hence,communication with a desired station can be executed without fail evenif a plurality of spread spectrum communication equipments using thesame PN code are used simultaneously.

The spread spectrum communication equipment, according to the presentinvention has a correlating means for detecting correlation between areceived PN code included in a receiving signal and a reference PN codegenerated in the transmitting side and outputting a correlation outputsignal, and a demodulating means for receiving and demodulating thecorrelation output signal. A timing generating means is provided forgenerating, in response to a correlation peak value existing in acorrelation output signal outputted from the correlating means, a timingsignal corresponding to the correlation peak value. A detecting meansdetects information of the correlation output signal outputted from thecorrelating means according to a timing signal from the timinggenerating means. An ID checking means receives the information detectedby the detecting means and checks whether the information coincides withthe ID code previously stored therein. A switching means providedbetween the detecting means and the demodulating means is provided forselecting connection or disconnection between the detecting means andthe demodulating means. The switching means selects connection ordisconnection thereof according to output of the ID checking means. Thetiming generating means receives a result of checking by the ID checkingmeans and generates, when the ID code does not coincide and also anothercorrelation peak value exists in a correlation output signal outputtedfrom the correlating means, a timing signal based on the latestcorrelation peak value. Hence, communication with a desired station canbe executed without fail even if a plurality of spread spectrumcommunication equipments using the same PN code are used simultaneously.

Although the invention has been described with respect to a specificembodiment for a complete and clear disclosure, the appended claims arenot to be thus limited but are to be construed as embodying allmodifications and alternative constructions that may occur to oneskilled in the art which fairly fall within the basic teaching hereinset forth.

What is claimed is:
 1. A spread spectrum communication equipmentcomprising:a correlator for detecting a correlation between a receivedPN code include in a received signal and an internally providedreference PN code, and, in response, outputting a correlation outputsignal; a timing generator for generating at least one timing signal inresponse to a correlation peak value existing in said correlation outputsignal; a plurality of detectors each detecting information of saidcorrelation output signal based on one of said timing signals generatedby said timing generator; a plurality of ID checking means eachreceiving information detected by said detector and checking whether theinformation coincides with a previously stored ID code; a demodulatorfor receiving and demodulating output signals of said plurality ofdetectors; a switch provided between said plurality of detectors andsaid demodulator for selecting connection or disconnection between saidplurality of detectors and said demodulator; and a controller responsiveto outputs of said plurality of ID checking means for selectingconnection or disconnection by said switch.
 2. A spread spectrumcommunication equipment according to claim 1, wherein said timinggenerator generates, when said correlation output signal indicating acorrelation peak value displaced by time t is inputted thereinto fromsaid correlator, timing signals t1, t2 having a PN cycle displaced bysaid time t according to displacement of this correlation peak value,and outputs either one of said timing signals t1, t2 to said detectors.